THE INFLUENCE OF FAT-FREE MASS ON PREDICTION OF DENSITOMETRIC BODY-COMPOSITION BY BIOELECTRICAL-IMPEDANCE ANALYSIS AND BY ANTHROPOMETRY

Objective: To examine the effect of varying size of fat free mass (FFM ) on the precision and bias of body composition prediction by bioelect rical impedance analysis (BIA) from four equations of Segal et nl (BIA -Segal), Gray et al (BIA-Gray), Lukaski et nl (BIA-Lukaski) and those from a manufacturer (BIA-EZC), by body mass index (BMI), and by skinfo ld methods with reference to estimation by densitometry, Subjects: 73 men and 77 women aged 17-71 years, were measured for height, weight, F FM, bioelectrical impedance and age. Results: BLA-Segal gave;the highe st precision (men: R(2) = 83%, women: R(2) = 75%) and the least bias ( men: slope = 0.88; women: slope = 0.81) of all BIA methods. There were poorer precision (R(2) less than or equal to 50%) and more bias (slop e <0.70) by BIA-Lukaski and BIA-EZC In both sexes, which were comparab le to the simpler BMI method, The skinfold method gave R(2) = 83% and slope = 0.84 in men and R(2) = 61% and slope = 0.86 in women. Bland an d Altman analysis showed BIA-Segal gave prediction of FFM within +/-6 kg of 95% confidence interval limit of agreement of that estimated by UWW in most subjects. Other BIA methods presented unacceptably large u nderestimates of up to 15-17 kg in FFM.Conclusions: The BIA-Segal prov ide the best predictions of the methods tested, but using BMI- or wais t-specific equations may be more practical than the original BIA-Segal method, which requires the subjects' % body fat to be known in order to apply the correct equation. Other BIA methods are affected by large FFM, and not better than anthropometric methods in predicting FFM.